Select no of cores without nodes and ppn

Hi all,

i want to select only the no of cores to be used instead of both the ppn and node.

Can anyone let me know how can i change the parameters in my job submission script.


The below statement can be used to submit jobs requesting only number of cores, but number of chunks would depend on the default_chunks set at the server level.
qsub -l ncpus=10 – /bin/sleep 10 # this would be scheduled on to a node which has 10 free cores.

The PBS Pro OSS , qsub chunk request system is as below (ppn and nodes are no more used )

qsub -l select=<number_of_chunks>:ncpus=:mem<memory_per_chunk> -l place=

Please check the below section from the
5.4.8 Platform-specific vs. Generally Available Resources

Hi Adarsh,

Thank you for the reply.

I have used the below script
#PBS -N test
#PBS -S /bin/bash
#PBS -q workq
#$#PBS -l nodes=2:ppn=5
#PBS -l select=1:ncpus=10
#PBS -j oe
NP=cat $PBS_NODEFILE | wc -l
mpirun -np ${NP} gmx_mpi mdrun -v -s md.tpr

But the job is being executed on single core.
After changing select=2 also still it is running only on 1 core.

Can you help me out.



Please use the below script

#PBS -N test
#PBS -S /bin/bash
#PBS -q workq
#PBS -l select=2:ncpus=5
#PBS -l place=scatter
#PBS -j oe
NP= `cat PBS_NODEFILE | wc -l\` mpirun -np {NP} gmx_mpi mdrun -v -s md.tpr


  1. mpirun path is set or same across the compute nodes
  2. the above script is run from a shared location accessible by all the nodes and the user running this script
  3. Please use absolute path in the script , unless there are no more than one flavour of mpirun (Intel/OpenMPI/Platformmpi)
  4. it the mpi is not integrated with PBS (compiling the mpi with PBS TM from source, then you might have use -hostfile or -machinefile pointing to $PBS_NODEFILE in the batch command line

Thank you

Thank you.

But again we are mentioning the nodes and cpus in different way here.
select=2:ncpus=5 instead of nodes=2:ppn=5

But i require to mention only no of cores, some thing similar to SGE script where we will mention only the no of core.



PBS syntax has been select/ncpus/mem (if i remember correctly since PBS Pro 11.x)
You can submit job as below

qsub -l ncpus=10 -- /bin/sleep

But the number of chunks (select bit) would be used from the server attribute default_chunk.ncpus. So you would be always requesting one chunk.

On the other hand:

  • you can write a queuejob hook that will convert the requested ncpus into select/ncpus/mem statement
    say you request
    qsub -l ncpus=120 -- /bin/sleep 100
    The queuejob hook will compose the select statement (based on some logic)
    qsub -l select=6:ncpus=20 -- /bin/sleep 100

Correction: (Thank you @agurban for this information)
PBS converts old-style resource requests to select and place statements.
See the 18.2 UG, section 4.8.3, "Conversion of Old Style to New", on page UG-70.